Lower back pain is a common type of pain in adults. There are many different causes of lower back-pain, such as degenerated discs having lost height hence causing nerve roots to be compressed between the vertebral bodies, or herniated nucleus portions pressing against nerves. However, in about 15% of the cases lower back pain is caused by irritation or inflammation of the sacroiliac joint (SI-joint). This joint connects the hip bones to the spinal column. In a first variant, lower back pain caused by the SI-joint is treated by non-surgical treatment, such as physical therapy, chiropractic manipulations, oral medications, injection therapy or intermittent use of a pelvic belt for symptomatic relief.
If a patient does not respond to conservative treatment, fusion of the SI joint is an option to eliminate the pain. To achieve fusion an implant is placed in the joint or across the joint, restraining the painful motion and causing both joint surfaces to grow together.
The SI-joint is characterised by being very irregular and having a three dimensionally curved joint surface. Furthermore, the bones being connected by the SI-joint, the ilium bone and the sacral bone, have very different bone quality. The ilium bone is much harder than the sacral bone. At the joint surface, both bones can be considered having substantially equal strength and rigidness. The combination of the shape and quality provides challenges for the implantation procedure and implant design.
Currently, a number of implant systems and techniques exist. One fusion technique is to screw multiple screws from the lateral side through the ilium bone into the sacral bone. The screws stabilize and compress the joint surfaces together, causing both bones to fusion over time. In an alternative technique porous elongated spacers are placed into the joint, promoting the fusion of the bones. However, placing such devices and screws bears a risk of damaging nerves that are located close to the sacral bone. These techniques are called lateral approach to the joint.
Another surgical approach to the joint is the posterior approach. In this technique, the joint is treated by entering from the posterior side or back-side of the joint. A large, conical and self-cutting hollow screw is placed between and through the joint surfaces. The screw cuts away and into the highly irregular curved, but stable joint surfaces, hence sinking into the bones and causing the joint to fuse. This approach is safe and stays away of neurovascular structures.
WO 2012/174485 (JCBD LLC) discloses a sacroiliac joint implant system having an elongated body and at least one fixation member or a pair of fixation members which extend outward from the longitudinal axis of an implant body. The implant system comprises a delivery tool having an implant body retainer including a drive shaft and implant body engagement shafts which are rotatably supported in a frame. The drive shaft is rotatably supported within the frame and comprises a geared portion engaged via a geared relationship with geared proximal ends of the engagement shafts such that a rotation of the drive shaft entails a rotation of the engagement shafts. Rotation of said engagement shafts allows threaded ends of the engagement shafts to be threadably received in threaded bores of the implant body such as to secure the implant body to the delivery tool.